TSI Level Test

Written by Gretchen Holm | Published on June 1, 2012
Medically Reviewed by George Krucik, MD

What is a TSI Test?

If you have hyperthyroidism, your thyroid produces too much of the thyroid hormones T3 and T4. This can lead to a range of symptoms, including fatigue, difficulty concentrating, nervousness, and restlessness.

When the symptoms of hyperthyroidism suddenly get worse, you have thyrotoxicosis. According to the Mayo Clinic, Graves’ disease is the most common cause of thyrotoxicosis, leading to over 60 percent of cases (Mayo Clinic). In this disease, your body produces thyroid-stimulating immunoglobulin (TSI). TSI mimics thyroid-stimulating hormone (TSH) and causes your thyroid to release excess T3 and T4.

Why Doctors Perform a TSI Test

Your doctor will typically order a TSI test if he or she suspects that you might have Graves’ disease, the most common cause of thyrotoxicosis. Your doctor may also routinely have this test performed during the final three months of pregnancy to help predict Graves’ disease in your body.

If you have Graves’ disease and the TSI in your bloodstream crosses into the placenta, it can result in your baby having what is called “transient neonatal Graves’ thyrotoxicosis.” This means that although your baby will be born with Graves’ disease, it is treatable and will pass after the excess TSI leaves his or her body.

Other disorders related to abnormal TSI levels include:

  • Graves’ disease: an autoimmune disease that causes your thyroid gland to produce excess levels of thyroid hormones (hyperthyroidism) including TSI.
  • Hashimoto’s thyroiditis: also called chronic thyroiditis, Hashimoto’s thyroiditis is inflammation and swelling of the thyroid gland, which often decreases the function of the thyroid gland (hypothyroidism).
  • Toxic multinodular goiter: with this, your thyroid gland is enlarged and has a number of small, round growths (nodules) that produce too much thyroid hormone.

The TSI Testing Procedure

Generally, you don’t need to do anything (such as fast or stop taking medications) to prepare for this test. However, if your doctor tells you to do so, follow his or her instructions. He or she may want to draw blood for other tests that require fasting at the same time as your TSI test.

When you arrive for the procedure, a healthcare provider will take a sample of your blood. The blood sample will be sent to a laboratory, where it will be tested to determine your TSI level.

Normal TSI Test Results

TSI test results are provided as a percentage. Typically, TSI test results of less than 130 percent are considered normal. Your doctor might have different standards, so you should ask if you have any questions or concerns.

What Do Abnormal TSI Test Results Mean?

Elevated TSI levels might indicate:

  • Graves’ disease
  • hashitoxicosis, which is increased thyroid activity caused by inflammation related to Hashimoto’s thyroiditis
  • neonatal thyrotoxicosis, in which your baby has high levels of thyroid hormones at birth because of your high levels; with treatment this will pass for your baby

Risks of Taking a TSI Test

This test itself doesn’t have any specific risks. However, there some risks involved with any blood test. For example, in rare cases, you might develop an infection or inflammation of the vein from which the blood was drawn.

More commonly, you can expect to feel minor pain during and shortly after the procedure. You might bleed a little bit after the needle is removed, and you could develop a small bruise in the area.

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